In Germany, the legal situation has been decided by the highest court:
"A software manufacturer can not enforce its interest in the fact that a program version offered at a favorable price is only sold together with a new PC, in such a way that it grants from the outset only one usage right limited in this sales channel the circulation or circulation of the manufacturer or with his consent, the transfer is free due to the exhaustion of the copyright distribution right regardless of its content restrictions of the granted right of use."
(I use a automatic translator. I hope it's understandable)
It simply means, that a license key that has been circulated once can be sold and used as long as it is only installed on one computer.